The functional encryption scheme is an encryption scheme that provides more sophisticated and flexible relations between an encryption key ek and a decryption key dk.
According to the functional encryption scheme, a parameter Φ and a parameter Ψ are respectively set in the encryption key ek and the decryption key dk. The decryption key dk can decrypt a ciphertext encrypted by the encryption key ek if and only if a relation R(Φ, Ψ) holds.
Non-Patent Literature 3 describes the functional encryption scheme.
Non-Patent Literature 6 describes the quadratic span program.